1. Field of the Invention
The present invention relates to the preparation of monohalohydroquinone monocarboxylates from hydroquinone monocarboxylates (more particularly of monochlorohydroquinone monocarboxylates from hydroquinone monocarboxylates), and to the use of such monocarboxylates for the preparation of monohalohydroquinone dicarboxylates and in particular monochlorohydroquinone dicarboxylates.
2. Description of the Prior Art
Monohalohydroquinone dicarboxylates and in particular monochlorohydroquinone dicarboxylates are important industrial compounds especially useful for the preparation of aromatic polyesters (cf. U.S. Pat. No. 4,118,372 and French Patent Application No. 79-24,135, published under No. 2,465,758) or as intermediates for the preparation of monohalohydroquinones, and especially of monochlorohydroquinone, which are employed as photographic developers (cf. U.S. Pat. Nos. 2,748,173 and 1,912,744).
Various methods for the production of monochlorohydroquinone dicarboxylates exist, which differ from each other in the nature of the starting materials. Thus, it has been proposed to prepare monochlorohydroquinone diacetate from benzoquinone. According to a first method, a reductive acetylation of chlorobenzoquinone is carried out [cf. J. Cason et al, J. Org. Chem., 15, 860-4 (1950)]. In a second method, simultaneous chlorination and reductive acetylation of benzoquinone are carried out by reacting the latter either with acetyl chloride, optionally in the presence of zinc [cf. Schied, Annalen, 218, page 213 (1883); G. A. Varvoglis, Ber., 70, page 2396 (1937); H. Burton et al, J. Chem. Soc., pages 2546-48 (1952)], or with acetic anhydride in the presence of zinc chloride [cf. Thiele et al, Annalen, 311, page 344 (1900); H. Burton et al, J. Chem. Soc., pages 755-59 (1952)]. These various methods are of no industrial interest, on the one hand because of their poor selectivity (they result in concurrent formation of large amounts of dichloro derivatives and of hydroquinone diacetate) and, on the other hand, because of the very fact that benzoquinone is used as a starting material. This is why the process of greatest industrial interest consists of preparing monochlorohydroquinone diacetate from hydroquinone, a common industrial product. This process comprises a stage of chlorination of hydroquinone to monochlorohydroquinone, followed by a stage of acetylation of the monochlorohydroquinone. This latter stage does not present any particular problem because the yields of monochlorohydroquinone diacetate are quantitative; the acetylating agent employed is acetyl chloride [Schied, loc. cit.]or acetic anhydride [cf. Levy et al, Annalen, 210, page 140 (1881); Van Herp, Ber., 58, page 664 (1925)]. On the other hand, the implementation of the chlorination stage is found to require more care, and the manner of carrying it out determines the quality of the final product. In fact, the various methods of chlorination of hydroquinone which have been used entail the concurrent formation of large amounts of dichlorohydroquinones which are difficult to separate from monochlorohydroquinone and which result in the formation of dichlorohydroquinone diacetates after acetylation, which are themselves also difficult to separate from monochlorohydroquinone diacetate. The problem of selective chlorination of hydroquinone to monochlorohydroquinone is an old one (cf. U.S. Pat. No. 1,912,744) and it to date has not been possible to solve it in a wholly satisfactory manner. In U.S. Pat. No. 2,748,173 it was proposed to carry out the chlorination of hydroquinone by reacting gaseous chlorine with a solution of hydroquinone in aqueous acetic acid; despite the precautions taken (use of a deficiency of chlorine which results in an incomplete degree of conversion of hydroquinone) the formation of dichlorohydroquinones remains high. In Japanese patent application published under No. 56/45,433 it was proposed to solve this problem by carrying out the chlorination with the aid of a 5N aqueous solution of hydrochloric acid in the presence of ferric or cupric chlorides and of a gas containing oxygen under pressure. Although this process makes it possible to restrict the formation of dichlorohydroquinones, its industrial interest is diminished by the need to operate under oxygen pressure and to require the presence of metal salts which promote the oxidation of hydroquinone to quinone.
As a result, serious industrial need still exists for a process for the preparation of monohalohydroquinone dicarboxylates in a selective manner, and more particularly for the preparation of monochlorohydroquinone dicarboxylates. Cf. U.S. Pat. No. 2,588,978.